2. The potential cooling of the soil’s thermal mass
The ground is regarded as a large reserve of solar energy. Its heat capacity is so important that the diurnal
variations of the surface soil temperature do not penetrate more than 0.5m, and seasonal variations not more than
4.0m in-depth. Beyond this depth, the temperature of the ground remains constant. The value of this temperature is
usually considered equivalent to the annual average solar temperature of its surface 2
.
The mass of the ground in lower part around, and sometimes also above a building can be useful in the majority of
the climatic areas like a source of natural cooling for the building, in a passive or active way. In summer, with a
depth of a few meters, the temperature of the ground is always below the average ambient temperature, and is
particularly below the temperature of the air during the day. As a result, the soil has the potential to serve as a
cooling source for buildings. Furthermore, it is possible by very simple means to lower the temperature of the earth
well below its normal temperature. The cooling surface, where the temperature of the soil surface is lowered,
induces a significant reduction in the temperature of the mass of earth which is below the surface.